The present invention relates to a preamplifier for a read and/or write head, and is more specifically related to an improved preamplifier for a magneto-resistive (MR) head for read and/or write operations.
Heads for reading and writing information are used in data storage systems, such as disc drives. Many data storage systems are designed for both the recording and the retrieval of data, and therefore require both a write and a read head. For example, conventional disc drives are used to both record and retrieve information. Typically, one head, a read/write head, is used for both the recording and the retrieval of data. The head is mounted on a head stack assembly (HSA), which typically includes a voice coil motor, an arm assembly, heads, a preamplifier, and a flexible circuit ("flex circuit") and flexible circuit board ("flex circuit board") that connects the heads, preamplifier, and printed circuit board together.
FIG. 1 is a perspective view of a conventional information storage system 10, hereinafter disc drive 10, having one or more heads 26 including a coil transducer, hereinafter coil head 26. The disc drive includes actuator arms 14 driven by a voice coil motor 16. The actuator arms 14 extend from a pivot assembly 20, located at one end of the voice coil motor 16, and over the discs 18 to position the coil head 26 over the selected track of one of the discs 18. The voice coil motor 16 responds to signals received at extension pins to provide the force necessary to rotate the actuator arms 14 about the pivot 20 to position the coil head 26 over a desired track on the rotating disc 18.
Each actuator arm 14 includes a substantially triangular shape rigid arm 12 and either one or two suspensions 30 supported by the rigid arm 12. The rigid arm 12 is mounted at the pivot 20 around which the actuator arm 14 rotates. The head 26 is mounted at the opposite end of the suspension 30 from the connection to the rigid arm 12. Referring to FIG. 3, each actuator arm 14 can support two suspensions 30, each supporting a head. One suspension 30b is for writing data to and reading data from the disc 18a above the actuator arm 14b, and the other suspension 30c is for writing data to and reading data from the disc 18b below the actuator arm 14c. The top and bottom actuator arms 14a, 14d only need one suspension, designated 30a and 30f, respectively.
Referring again to FIG. 1, each of the coil heads 26 reads data from and writes data to selected tracks on the surface of the disc 18. The position of the heads 26 is determined by the voice coil motor 16 which responds to electrical signals from a controller (not shown) supplied through a preamplifier 22. Only one head can read or write data at a time. The preamplifier contains a MUX and DEMUX circuits to select which of the heads is operating. The data read from the tracks on the disc 18 is also transferred through the preamplifier 22. The preamplifier amplifies the signals and transfers them to external circuitry. The preamplifier is connected by a flex circuit 24 to each of the actuator arms 14. Typically, only one preamplifier is used, however, if there is a large disc stack several preamplifiers can be used, with each preamplifier connected to only some of the actuator arms. In disc drives 10 where the head 26 contains a coil transducer, the preamplifier 22 is typically located on a base board adjacent to the actuator arm 14, as in FIG. 1, which places it typically 31/2 to 4 inches away from the head 26 in a 31/2 disc drive.
Magneto-resistive (MR) heads have become popular in disc drives because they allow for an increase in the density with which data can be stored on the disc and they allow an optimization of the read and write operations. FIG. 2, shows a conventional disc drive 10' having a head 40 including an MR transducer, hereinafter an MR head 40. Disc drive 10' again includes a plurality of actuator arms 14 that extend over the disc 18 from a pivot assembly 20, located at one end of a voice coil motor 16. The actuator arms 14 are driven by the voice coil motor 16 to position the MR head 40 over the selected track of the disc 18. The voice coil motor 16 responds to signals received at extension pins to provide the force necessary to rotate the actuator arms 14 about the pivot 20 to position the MR head 40 over a desired track on the rotating disc 18. The position of the MR head 40 is determined by the voice coil motor 16 which responds to electrical signals from a controller (not shown) supplied through a preamplifier 50. Only one of the heads operates at a time. The preamplifier 50 contains a MUX and DEMUX circuits to select which of the heads is operating. The data read from the tracks on the disc 18 is also transferred through the preamplifier 50 where the signal containing the data is amplified and is transferred to external circuitry.
Each actuator arm 14 includes a substantially triangular shaped rigid arm 12 and a suspension 30 supported by the rigid arm 12. The rigid arm 12 is mounted at the pivot 20 around which the actuator arm 14 rotates. The MR head 40 is mounted at the opposite end of the suspension 30 from the connection to the rigid arm 12. Again, each actuator arm 14 can support two suspensions 30, one for the disc above the actuator arm 14 and the other for the disc below the actuator arm 14. The top and bottom actuator arms 14 only need one suspension 30. Also mounted on the actuator arms 14 is a flex circuit board 42, which is connected by a flex circuit 48 to a base circuit board 44.
FIG. 4 is a block diagram of a conventional preamplifier 50. The preamplifier 50 contains write drivers 52 and a read amplifier 54 (a read output buffer). The preamplifier 50 also typically contains logic 60, such as the head select and mode control circuit 60 that controls the operation of the preamplifier 50, a fault detection circuit 62 that contains write and read fault detection circuitry, a MUX 66 and DEMUX (not shown), a serial interface control 70, write 64 and read bias 72 circuits, a bandgap circuit (not shown), a voltage detection circuit (not shown), circuits to obtain thermal and current measurements of the MR transducer (now shown), and several D/A converters that are shown as parts of the other blocks. The preamplifier 50 may also include various other circuitry (not shown).
Referring again to FIG. 2, the signal line impedance between the transducer of the MR head 40 and the preamplifier 50 is critical when using low impedance preamplifiers 50. The signal line impedance if the preamplifier 50 was placed on the baseboard adjacent to the actuator arm 14 would result in a significant reduction in bandwidth for a low impedance preamplifier 50. Additionally, the attenuation of the signal if the preamplifier 50 was placed on a base board adjacent to the actuator arm 14 could result in a loss or corruption of data. Placing the preamplifier as close to the heads as possible reduces the inductance between the head and the preamplifier, since the length of the wire is shorter. Reducing the inductance allows for an increase in frequency, producing an increase in the bandwidth, during a write operation, thus increasing the maximum data rate and capacity. It also reduces the power consumption during a write operation.
The preamplifier 50 should be mounted as close as possible to the MR head 40 so that the preamplifier 50 can receive a strong signal from the head 40. However, for other reasons, such as the size of the preamplifier and cost of mounting, it may be desirable to mount the preamplifier 50 elsewhere. The preamplifier 50 can be mounted in one of three places. It may be bonded directly to the top rigid arm 12 in a position similar to location 46. It may be positioned on the flex circuit board 42, which is attached to actuator arm 14. Finally, it may be mounted to base circuit board 44, which is attached to the base casting 28 of disc drive 10'. When the preamplifier 50 is mounted to the top rigid arm 12 it is farther from the head 40 of the bottom actuator arm 14 than if the preamplifier 50 is mounted on the flex circuit board 42.
Referring to FIGS. 2 and 3 simultaneously, in an MR head, it is preferable to mount the preamplifier 50 to the flex circuit board 42. For a 31/2" disc drive, the signal run length from the MR transducer to the preamplifier 50 on the flex circuit board 42 is about 11/2" to 13/4", saving about 2 inches over placement of the preamplifier circuit on the baseboard adjacent to the HSA.
The preamplifier is mounted on the flex circuit board 42 or the top rigid arm 12 because that is the closest that the preamplifier 50 can be mounted to the MR head 40. However, due to the signal bandwidth reduction of the MR heads, it is desirable to move the preamplifier closer to the MR heads.